import java.util.*;

class Solution {
    List<List<Integer>> ret;
    List<Integer> path;

    public List<List<Integer>> subsets(int[] nums) {
        ret = new ArrayList<>();
        path = new ArrayList<>();

        dfs(nums, 0);
        return ret;        
    }

    public void dfs(int[] nums, int pos){
        ret.add(new ArrayList<>(path));

        for(int i = pos; i < nums.length; i++){
            path.add(nums[i]);
            dfs(nums, i + 1);
            path.remove(path.size() - 1);  //恢复现场
        }
    }
}